Conventional optical channel monitoring in planar waveguide circuits (PLCs) used for fiber-optic communication is usually implemented separately outside of the PLC product packaging; resulting in more complex integration of optical channel monitoring within an optical network. If the optical channel monitoring function is integrated into the PLC components, special PLC design is necessary, and the entire PLC component package should be hermetically sealed to protect against any moisture-related reliability concerns typically associated with semiconductor photodetector devices.
For example, if external optical channel monitors are considered, they require separate packaging from the PLC packaging; and optical path connection via optical fiber splicing, or other optical connectorization external to the PLC and fiber array units (FAU) which provide the fiber connection to the PLC along the PLC chip edge(s). The size of entire packaging will be increased, and optical connection paths also increase. Photodetectors as well as low-loss, zero-slope fused coupler components are necessary, requiring at least two fused splicing operations. This results in higher costs, larger size, and tedious assembly.
Power monitor detector chips inside the PLC packaging, attached directly to monitor waveguides along the edge of PLC chips, are also possible. However, this requires specially-designed PLCs, with dedicated monitoring channel waveguides (tapped on-chip from the operational waveguides) to drive the power monitor detectors attached to the chip. The detectors are separate from the fiber array unit(s) (FAUs) which always require attachment to the operational waveguides along the edge of the chip for network functionality. In this case, conventional off-the-shelf PLC chips cannot be utilized, because they usually will not have separate monitor waveguides. Also, the separate optical power monitor detector chips require anti-moisture environmental protection to provide long-term reliability. Special techniques are necessary to attach the detector chips to the edge of the PLC chip, aligned with the monitor waveguides. And, the entire PLC packaging still requires hermetic packaging which increases the packaging costs dramatically.
The present invention addresses these problems, by providing a power monitoring function, integral to the fiber array unit, requiring no special PLC re-designs, and facilitating hermetic sealing.